Thanks for starting this thread, Ian. Apologies for being a bit slow to add my few cents' worth -- am just back from a nearly-end-of-winter break on the Pacific coast of Costa Rica. (A useful spot to check out sun protection, though it wasn't for that reason we went there.

)
I'm a member of the Spotted Tribe -- my mum's family is Scots-Irish, and I've inherited her sensitivity to UV rays. (This of course lets me check in occasionally with Shaun Pollock and Rod Laver & exchange notes & wisdom.)
As for sources of cycle clothing: Over the past ten years or so, I've come to rely almost entirely on Ground Effect in New Zealand, here:
https://www.groundeffect.co.nz/I've found their products first-rate for quality, fit and comfort. Prices are reasonable, too -- not least because postage from NZ is very inexpensive by comparison with, say, Canada or the U.S. I now have only GE garments for my longsleeved cycling jerseys (specifically the "Rock Lobster"), and I have a couple of "Berglar" T-shirts for indoor wear & under-clothing. GE advertises a UPF of 50 for their jerseys.
I also have a rainwear jacket, the "Anti-Cyclone". (I should say that GE has an apparently endless stock of product names. Most of these I enjoy, and I had a cheerful conversation with them about their use of "Zamboni",. something dear to every Canajan I know. Others are less, er, successful: The rain jacket one step down from mine is named the "Storm Trooper".)
I've also found GE cycling shorts to be very comfortable. I usually wear a pair of their liner short under loose overshorts. For the latter, I use hiking shorts sourced in Ottawa, usually below the knee.
An alternative source for over-the-knee knickers is an outfit named AeroTech Designs, in Pittsburgh, Next Door. I have a pair I bought years ago, and wear them often. They sell a pair for USD 65 these days (about CAD 100) + extortionate postage. That's a very reasonable price for a quality garment, but I doubt I'll buy anything from them for a while, on account of The Situation. (In times past I would use a friend's address in NYC when ordering, and collect them when we visited, but again, that option is off the table for now.)
Hope this is helpful, Ian, and good luck.
Cheers, John